TNF-alpha, and other members of the TNF ligand superfamily, play an important role in the pathogenesis of many forms of lung disease. Receptors for these ligands lack enzymatic domains and initiate signal transduction by recruiting secondary proteins, predominately death domain (DD) proteins that activate programmed cell death (apoptosis) or TNF receptor associated factors (TRAF 1 to 6) that may act as intermediaries to prevent apoptosis and regulate transcription factors NFkB and AP-1. Despite the importance of TNF-alpha and other ligand/receptor pairs functionally dependent on TRAF associations, in pulmonary disease, little is known about the expression or function of TRAF proteins in the lung such that the proposed study is both novel and significant. Although many aspects of TNF receptor (TNFR) signaling in the lung remain to be studied, the current proposal is focused to TRAF1 for several reasons: 1) it is expressed only in lung, spleen, thymus and testes suggesting tissue specific function, 2) it is highly regulated in lung cells, while TRAF2-6 are ubiquitously and constitutively expressed, 3) it forms heterodimers with other TRAF proteins and is essential for docking of added second messenger proteins to TNFRs suggesting a role as modulator of signal transduction pathways and 4) clinical significance is suggested by the demonstration of increased TRAF1 protein in human neonatal lung disease and in mice exposed to IT TNF-alpha or hyperoxia. Current evidence indicates that TRAF1 functions as an adapter protein between TNFRs, TRAF2 and proteins that inhibit apoptosis or activate NIK and JNK/SAP kinases. Preliminary data and recent studies suggest that TRAF1 inhibits TNF-alpha induced apoptosis and modulates induction of transcription factors NFkB and AP-1. The central hypothesis of the current proposal is that TRAF1 is induced in the lung by TNF-alpha in an NFkB dependent manner and that the increase in TRAF1 results in decreased apoptosis of lung cells and altered gene expression contributing to epithelial cell hyperplasia, inflammation and fibrosis. The proposed studies will demonstrate the cellular function of TRAF1 in vitro and the role of TRAF1 expression in vivo in transgenic overexpression and ablation models stressed by hyperoxia.